Category: Astrophysics

Physics is traditionally viewed as a hard subject requiring a great deal of mathematical prowess, devotion and perseverance to muster the subject matter. To a large extent, it is definitely true. But it does also offer, in its turn, a great deal of satisfaction, excitement and sense of achievement.

The 21st century physics, spanning from quantum computing to super-thin layer material called graphene to ultra-efficient LED bulbs to efficient harnessing of renewable energies to black holes to dark matter and dark energy, the range of topics is endless and it will disappoint no one with its vast challenges and ensuing excitement.

In our day-to-day lives, we encounter matter comprising protons and neutrons bundled together at the centre, called nucleus, of an atom and electrons whizzing around the nucleus. Some decades ago, these protons, neutrons and electrons were thought to be the fundamental particles of all matter; but not anymore. Now, quarks (six types) are thought to be the fundamental matter particles, which are glued together by force particles to form protons and neutrons.

These atoms and molecules making up matter here on earth are what we are accustomed to. The laws of physics, or for that matter of natural sciences, were developed to explain the natural processes as we encounter in our lives.

The basic physical principles are like these: a body has a definite size comprising length, breadth and height; it has a mass and weight; it is visible when there is sufficient light. If we push a body, we impart momentum, which is the product of mass and velocity. As it has the mass, it has gravity, meaning it attracts every other body and every other body attracts this body. These are the basic properties of a body as described in classical physics.

But there is no reason to be dogmatic about these basic principles. These principles can change here on earth or in our galaxy or somewhere outside our galaxy. When they do change, we would feel that things have gone topsy-turvy.

We live on a very tiny planet, called Earth, which revolves round the star, called Sun. There are eight other planets, thousands of satellites, comets and asteroids, all held together by the gravity of the Sun. The Sun, though extremely bright and overwhelmingly powerful to us, is a small star in our galaxy, called the Milky Way. It is estimated that there are over a billion, yes, 1,000,000,000 stars, many of them are much bigger than the Sun, in our galaxy. Now our galaxy is by no means the biggest or dominant galaxy in the universe. Cosmologists estimate that there are around one billion galaxies in our universe! Some of these galaxies are hundreds or even thousands of times bigger or massive than our galaxy. There are massive black holes at the centres of most of the galaxies, exerting gravitational pull to keep the galaxy together. Some of these black holes are millions of times bigger than the Sun. Now we can have a feel of how big our universe is!

Physics, or more appropriately astrophysics, studies the processes of these vast expanse of celestial bodies. The Sun as well as our galaxy, the Milky Way having over a billion stars are not static. The stars are spinning, the galaxy is spiralling, and everything is in motion.

Strange glow from the centre of the Milky Way

It was estimated, purely on physical principles, that the stars at the edges of a galaxy should move slower than the central ones, as the force of gravity of the galaxy is weaker away from the centre. But astronomical observations show that stars orbit at more or less at the same speed regardless of their distance from the centre. That was a great surprise, indeed shock, to the astrophysicists. The way this puzzle was eventually tackled was by assuming that there are massive unseen matters that exert tremendous amount of gravitational pull to keep the outlying stars moving at nearly the same speed and that mysterious matter is called the dark matter.

There are other tell-tale signs that there is something amiss in the material accounting of the universe. A strange bright glow spread over the length of the Milky Way was thought to be due to ordinary pulsars (pulsating stars) along the length. But now it is thought that dark matter may be responsible for this glow! But how does it do that, physics does not know yet.

But is this dark matter a fudge to solve the apparent conflict of physical behaviour with observations? Not really, this is how science progresses. Well thought out ideas are advanced and those ideas are tested and cross-examined against observations and the idea or concept that passes the tests is taken as the valid scientific concept.

But how do we know dark matter is there, if we cannot see them. We cannot see them because dark matter does not interact with light or electromagnetic radiation such as visible light, infra-red, ultra violet, radio waves, gamma rays and so on. Light goes straight through the dark matter, as if it is not there.

It should, however, be pointed out that dark matter is not the same thing as black hole. A black hole is made up of everyday particles (matter particles and force particles) – electrons, protons, neutrons, atoms, molecules, photons etc. Its gravity has just become so strong (because of its mass and super-compacted size) that it pulls and crushes everything to its core and nothing can escape from its clutches, not even light! A beam of light coming close to a black hole is pulled right insight and that is the end of that light beam never to be seen again!

Dark energy expansion

Dark matter, although invisible, does exert gravitation pull and this gravitational pull that makes dark matter attractive to scientists. The Universe, although expanding, is not in danger of runaway expansion. There is something that is holding the whole thing together and that something may be the dark matter.

Immediately following the Big Bang, the then Universe expanded very rapidly, known as inflationary phase, for tens of millions of years followed by expansion for some billion years and then it stabilised for a few billion years and now it is again in the expansion phase. The present expansion is that the space itself is expanding and so every star and every galaxy is moving away from every other star or galaxy. What is giving these celestial bodies energy (repulsive in this case) to move away from each other? Scientists came up with the proposition that there must be some unknown, unseen energy, which is now called the dark energy.

On
purely material and energy balance of the Universe, it is thought that our
visible (and known) Universe accounts for only 4.9 percent of the total
Universe, dark matter accounts for 26.8 percent and dark energy for 68.3
percent. So, we only know in the vast mind-boggling universe extending over
13.8 billion light years a meagre 5 percent and the remaining 95 percent is
hidden or unknown to us!

Scientists all over the world are trying hard to find evidence of dark matter and dark energy. CERN’s Large Hadron Collider (LHC) is trying to find any remotest evidence of dark matter and energy. On theoretical basis, some scientists are proposing that dark energy may emanate from a fifth form of force, which is yet unknown. The four forces that we know are electromagnetic, weak nuclear, strong nuclear and gravitational forces. The fifth force may be a variant of gravitational force – a repulsive gravitational force – that comes into play in the vast intergalactic space.

When Einstein produced the general theory of relativity in 1915, he introduced, almost arbitrarily, a parameter, called the cosmological constant, into the theory to counter the effects of gravitational pull and make the Universe a static one. That cosmological constant effectively introduced the repulsive effects. It may be pointed out that the Universe was thought to be static at that time. But only a few years later when it was incontrovertibly shown that the Universe was, in fact, expanding, Einstein humbly admitted that it was his “biggest mistake”. Now, more than hundred years later, it is assumed that the cosmological constant may be considered to be the quantity to cater for the dark energy! Could Einstein’s “biggest mistake” be a blessing in disguise, it offers not only a correct presumption but also a saviour of modern cosmology?

A black hole – hitherto an invisible celestial body – was in cosmological vocabulary even before Einstein’s theory of relativity in 1915. But when the relativity theory predicted with full scientific rigour that a massive stellar body can have such a strong gravitational pull that nothing, no object, not even electromagnetic radiation such as light, can escape from it, the concept of a black hole became firmly established in scientific parlance. But it remained at that time only a mathematical curiosity, as no scientific evidence or mechanism of formation of a black hole was put forward. However, it became a realistic possibility after the detection of pulsars some decades later.

The detection of pulsars (rotating neutron stars) by Jocelyn Bell Burnell, a research student at the University of Cambridge in 1967, gave renewed spurt to the concept of gravitational collapse and the formation of black holes. A normal star, when it comes to the end of its life due to lack of fusion fuel, collapses under its own gravity and becomes a neutron star. It may be mentioned that an atom consists of neutrons (neutral in charge) and positively charged protons and negatively charged electrons. If gravity becomes too strong, protons and electrons are pulled together to merge with each other, neutralise their charges and become neutrons and the whole star becomes a neutron star. (For the detection of neutron star, which was considered as “one of the most significant scientific achievements of the 20th century” by the Nobel Committee, her supervisor and another astronomer were awarded Nobel prize in Physics in 1974, but Jocelyn Bell was not even mentioned in the citation. However, years later, in 2018, she was awarded the Special Breakthrough Prize in Fundamental Physics. She donated the whole of the £2.3 million prize money to the Institute of Physics in the UK to help female, minority, and refugee students become physics researchers.

Not all stars eventually become neutron stars. If the mass of a
star is less than 2.6 times the mass of the Sun, the gravity would not be
strong enough to turn it into a neutron star. The gravitational pull in a
neutron star ultimately becomes so strong that all its mass and its nearby matters
are pulled to a small volume and the star becomes a black hole. A black hole
can merge with another black hole to become a bigger and stronger black hole.

It is speculated that there are black holes of various sizes in
most of the galaxies and in some galaxies, there are supermassive black holes
at their centres. The nearest black hole from Earth is quite a few thousand
light-years away; but they exert no influence on this planet. The supermassive
black hole in our galaxy (the Milky Way) is about 26,000 light-years away.

Despite the name, a black hole is not all black. The gas and dust trapped around the edges of the black hole are compacted so densely and heated up so enormously that there are literally gigantic cauldrons of fire around the periphery of a black hole. The temperatures can be around billions of degrees!

The first direct visual evidence of a black hole had been produced on 10 April 2019 by a team of over 200 international experts working in a number of countries. The Event Horizon Telescope (EHT) was used to detect the existence of a colossal black hole in M87 galaxy, in the Virgo galaxy cluster. The computer simulation from data collected in the EHT is shown below. This black hole is located some 55 million light-years from the Earth and its estimated mass is 6.5 billion times that of the Sun! So, this black hole is truly a monster of a black hole.

Computer simulation of black hole from real data

Although it is a monstrous black hole, its size is quite small
and it is enormously far away (520 million million million kilometres away) from
Earth. To observe directly that elusive black body that far away, astronomers
require a telescope with an angular resolution so sharp that it would be like
spotting an apple on the surface of Moon from Earth and the aerial dish that
would be required for such a detection would be around the size of Earth!
Obviously, that is not possible.

Instead, the international team of experts devised a Very Long Baseline Interferometry (VLBI) technique, which involves picking up radio signals (wavelength 1.3 mm) by a network of radio telescopes scattered around the globe. The locations of these eight radio-telescopes are shown below. When radio signals from these radio-telescopes are joined up, taking into account their geographical locations, lapsed times for signal detection etc, and processed in a supercomputer, an image can gradually be built up of the bright part of the periphery of the black hole.

Locations of Event Horizon Telescopes (EHT)

The
key feature of a black hole is its event horizon – the boundary at which even
light cannot escape its gravitational pull. The size of the event horizon
depends on the mass of the black hole. Once an object crosses the boundary of
the event horizon, there is absolutely no chance of coming back. A lead
astronomer from MIT working on this EHT team said, “Black hole is a one-way
door out of this universe.”

The
general theory of relativity also predicted that a black hole will have a
“shadow” around it, which may be around three times larger than the event
horizon size. This shadow is caused by gravitational bending of light by the
black hole. If something gets nearer the shadow, it can possibly escape the
gravitational pull of the black hole, if its speed is sufficiently high
(comparable to the speed of light).

It
is postulated that the “shadow” comprises a number of rings around the event
horizon. The nearer a ring is to the event horizon, the more rigorous and compact
it is with extreme pressure-temperature conditions.

If, hypothetically, an unfortunate human being falls even into the outer ring of a “shadow”, he will be pulled towards the black hole initially slowly and then progressively strongly – his leg will be pulled more vigorously than his upper part and consequently, his body will be deformed into a long thin strip like a spaghetti. And when that spaghetti shape crosses the event horizon, it will be stretched so much that it will become a very thin and very long string of atoms!

Is wormhole the link between a black hole and a white hole?

The
general perception of a black hole is that it is a monster vacuum cleaner where
everything, even light, is sucked into it through a funnel and nothing,
absolutely nothing, can come out. It absorbs enormous amount of matter and
squashes them into tiny volumes. What happens to this gigantic amount of matter
is a mystery, a black mystery.

There
are two parallel streams of pure speculative thoughts. One is that when a black
hole becomes too big – either by incessantly swallowing up matters from its
surroundings or by merger with other black holes – a super-giant explosion,
more like a big bang, may take place. So, a black hole may be the mother of a new
big bang, a new generation of universe.

The other thought is that the funnel of a black hole is connected through a neck, called the wormhole, to a different spacetime and hence a different universe at the other end. All the materials that a black hole sucks up at the front end in this universe go through the wormhole to another reverse funnel where all the materials are spewed out into a different spacetime. That funnel is called the white hole. Thus, a black hole and a white hole is a conjugate pair – a connection between two universes! But the question is, since there are billions of black holes in our universe, then there could be billions of corresponding wormholes and white holes and universes.

One universe is big enough or bad enough for human minds to contemplate, billions of universes will make humans go crazy.

Summer
1666, a young Cambridge University physics student by the name Isaac Newton was
sitting under an apple tree in his mother’s garden at Woolsthorpe Manor in
Lincolnshire, England. An apple fell from the tree on the ground and that triggered
him to think: why did the apple come down straight to earth, not go sideways or
upwards? That question led him to delve deeper into the mystery of attraction
between two bodies and to come up with the law of gravity. He published his research
work in “The Principia Mathematica” in 1687, where he described, among other
things, this seminal work on the law of universal gravitation.

This law of gravitation tells us that two bodies attract each other with a force which is proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between them. This simple empirical formula was astonishingly successful in calculating the force of attraction between two bodies on earth. This law was also applied to calculate the attractive force between the earth and the moon and to the orbital motion of the moon round the earth. The law was quite accurate in defining the orbits of many other celestial bodies, although in few cases the law was somewhat inaccurate.

This
law was and still is the centre piece of what is now known as the ‘classical
physics’ or ‘Newtonian Physics’. We all studied this law, Newton’s laws of
motion, properties of matter, electricity and magnetism, heat and
thermodynamics, optics etc in our schools and they gave the grounding for
advanced physics.

For nearly 300 years this law was supreme and explained how the force of gravity controls the motions of all celestial bodies. However, the law did not say anything about the nature of this force or how the force is propagated through space; it just stated that the force diffuses through space without leaving any trace. As the predictions of the law were right in most of the cases, nobody bothered too much about these minor details or even ignored some minor discrepancies.

At the turn of the 20th century, a patent clerk by the name Albert Einstein was working on patent submissions of electrical devices in Bern, Switzerland as a ‘Technical Expert, Third Class’ and in his spare time he was working on gravitational problems. The Patent Office work took up 48 hours of his time per week over six days. Einstein described his work load subsequently as, it left him with ‘eight hours for fooling around each day and then there is also Sunday!’.

In 1905 he published a technical paper outlining the Special Theory of Relativity giving revolutionary scientific ideas and concepts. In this paper, he introduced two fundamental concepts: the principle of relativity and the constancy of speed of light. The speed of light was stated to be independent of the speed of the observer. In other words, whether the observer moves in the direction of light or opposite to it, he would see the speed of light always remaining constant (c= 3*108 m/s). (It may be mentioned that in 1905, Albert Einstein produced three more monumental papers of enormous significance: (i) the mass-energy equivalence (E=mc2), (ii) Brownian motion of small particles, and (iii) photoelectric effects. For his work on photoelectric effects showing the particulate nature of light, which laid the foundation for quantum mechanics, he was awarded Nobel prize in 1921. As mentioned above, the year 1905 was extremely productive for Albert Einstein.

Visualisation of Einstein’s spacetime construct

Einstein
developed his relativity concept even further and produced the General Theory
of Relativity in 1915. In this General Theory of Relativity, he advanced the
principle of spacetime, not space and time. He stipulated that the three
dimensions of space (such as X, Y and Z dimensions of cartesian coordinates)
and one dimension of time are not independent of each other, but intricately
linked to form a single four-dimensional spacetime continuum.

This
concept of spacetime continuum was revolutionary at that time and even now they
make human beings baffled. The relativistic consideration has produced what is
now called the time dilation. The passage of time is relative and so it depends
on the motion of an observer relative to a stationary observer. Also, the
passage of time depends on the location in a gravitational field. For example,
a clock attached to an observer in a spaceship will tick slower than that of a clock attached to an observer in a stationary position. Also, a clock in a higher gravitational field, such as at the surface of earth, will tick slower than that of a clock in lower gravitational field such as the top of a mountain.

Let’s
take an example. There were three men in the UK, all of them exactly of the
same age, say, 25 years. They decided to offer themselves as guinea pigs for a
research on gravity. One was asked to stay in Lincolnshire, England (not too
far from Newton’s famous apple tree), the other was told to go and live high up
in the Himalayan mountains and the third, most adventurer of the lot, got the
opportunity to have a space travel in a superfast spaceship. The spaceship travelled
fast and so his clock was ticking slowly. Let’s say his spaceship was so fast
that one year in the spaceship clock was equal to five earth years and the
mountain man clocked 10 minutes more than the Lincolnshire man in five years.
When after five years they met on earth, they found that the mountain man was
10 minutes older than 30 years, Lincolnshire man was 30 years of earth age and
the spaceship man was whopping four years younger than 30 years! To the
spaceship man, it would look like he had come back four years in the future!

Einstein
stipulated that the gravitational field creates space and the bodies with
masses bend and warp space; more like massive bodies create curvature in a
trampoline. All less massive bodies fall into the curvature in the trampoline
created by the massive bodies. When there are a large number of bodies warping
the space, the space becomes jagged and celestial bodies move around in
tortuous paths. There is no force of gravity pulling objects towards each other;
just the bodies move around the jagged curved space along the path of least
resistance.

Space, like any other force field, is discreet, quantised and granular. The quantum of space is dubbed as graviton, similar to the term photon in electromagnetic field, and it is so small that we cannot feel its discreteness, as we cannot feel the discreteness of photons of light or discreteness of atoms in a solid body.

Exactly
hundred years after Einstein’s General Theory of Relativity, experimental
evidence of gravitational field and gravitational wave have been produced by
the LIGO (Laser Interferometer Gravitational-wave Observatory) experiment and
shown that space is modulated by the gravitational field. A monochromatic laser
beam of light was split and sent at right angles to each other along two arms,
each of 4 km long. These beams were reflected back along the same path and
allowed to interfere back at source. If there is no distortion or modulation of
the path lengths, the two beams would interfere in anti-phases and there would
be no interference patterns.

When two super massive black holes some 1.3 billion light years away merged and produced a gigantic massive black hole, an enormous amount of energy, equal to three solar masses, was produced and sent out as gravitational energy. It rippled through the whole universe in the form of gravitational wave at the speed of light and deformed the spacetime fabric. That deformation in spacetime was detected by the LIGO experiment in the form of interference pattern and that proves that gravitational waves modulates the space.

The
implication of Einstein’s spacetime is that at the very beginning when even the
‘Big Bang’ did not take place, there was no spacetime. Spacetime came into
existence following that ‘Big Bang’, when gravity came into play along with
other forces such as electrical force, strong nuclear force and weak nuclear
force. If at the end, as Physics predicts, the whole universe starts to
collapse, there would be what is called the ‘Big Crunch’ and the spacetime
would collapse too and disappear. There will be nothing, no material, no space
and no time. These are the predictions of scientific theories as exist today.

In 1930 when Einstein came to London as the guest of honour at a fundraising dinner to help the East European Jews, George Bernard Shaw, the chief guest, said humourously, “Ptolemy made a universe which lasted for 1400 years. Newton made a universe which lasted for 300 years. Einstein has made a universe, and I can’t tell you how long that will last.” The audience laughed loudly, but none louder than Einstein.

The quantum concept that came into existence precisely in the year 1900 was both revolutionary in outlook and spectacular in outcome. This very concept which was put forward by Max Planck in 1900 when he tried to explain black body radiation was subsequently taken up by a luminary like Albert Einstein (as yet unknown to the world) in 1905 and gave a rational explanation to the hitherto difficult scientific problem.

The classical physics (also known as Newtonian physics) was ruling the day until about 1900 when all day-to-day physical problems could be explained by this discipline. But gradually it was running out of steam as new technically challenging phenomena came up due to invention of new instruments and reliable measurements were made.

The
intractable physical processes like the black body radiation, interactions of
light with particles, the puzzling behaviour of light and many more physical processes
could not be explained by traditional classical mechanics. So, a new method, a
new mode of thinking, a new science had to be invented that would explain all
these inexplicable things.

Although Max Planck was first to venture outside the conventional concept of light being wave in nature to explain ‘black body radiation’ in 1900, it was Albert Einstein who gave scientific explanation by proposing in 1905 the ‘quantisation’ of light – a phenomenon where light was assumed to consist of discreet packets of energy – which he called quantum of light or photon. This quantum of light was advanced in order to explain the hitherto inexplicable photoelectric process, where light was allowed to fall on the surface of a metal and electrons were detected to have emitted. No matter how long or how intense one type of light was, electrons would not be emitted. Only when light of higher frequencies was allowed, electrons were emitted. Einstein showed that photons (quantum of energy in a bundle) of higher frequencies have higher energies and those higher energy photons could emit electrons. (It was like, no matter how long or how heavy the rain is, the roof would not be dented. Only when hailstorm of sufficient big sizes falls on the roof, does the roof cave in). For this quantisation theory, Einstein was awarded Nobel prize in 1921.

Thus, light came to be viewed as both wave and particle, depending on experimental circumstances, and hence the nomenclature ‘wave-particle duality’ came into common vocabulary. If hitherto electromagnetic light can be viewed both as wave and particle, can particles (like electrons) behave like waves? Indeed, so. If electrons are allowed to go through two slits, they interfere and produce alternate bright and dark spectral lines on a screen, exactly like light waves do. The microscopic world does not distinguish between waves and particles, they are blurred into indistinguishable entities. That is the nature that quantum mechanics has produced.

Although Einstein was the pioneer of quantisation of light, he was not at ease with the way this new concept had been taken up by ‘new lions’ under the stewardship of physicists like Niels Bohr, Wolfgang Pauli, Werner Heisenberg, Erwin Schrodinger, Max Born and many more in the early part of the last century. They collectively produced the full-blown quantum mechanics, which Einstein had difficulty in recognising.

In
quantum theory, particles like electrons revolving round the nucleus of an atom
do not exist as particles. They are like strata of waves smeared round the
nucleus. However, they exist, behaving like particles, when some energy is
imparted to the atom or some energy is taken away from the atom resulting in
those electrons moving up or down in energy levels. In other words, electrons
exist only when there is an interaction or transition. Without such transitions,
electrons just do not show up. However, electrons (with negative charge) are there
around the nucleus, but there is no way of telling where the electrons are –
only probability of their presence (wave function) can be described! No wonder,
Einstein was not happy with such description, which he called incomplete.

Heisenberg
produced what came to be known as ‘Heisenberg uncertainty principle’. The
elementary particle like an electron cannot be measured with absolute accuracy
both its position and momentum at the same time. The act of measuring the
position of an electron disturbs the complementary parameter like velocity and
so certain amount of uncertainty in momentum creeps in – that is the
uncertainty principle. Similar uncertainty exists when measuring time and
energy of the particle at the same time.

Niels Bohr, the high priest of quantum mechanics, produced from his Advanced Institute of Physics in Copenhagen, what came to be known as ‘Copenhagen Interpretation’ of quantum mechanics. This interpretation advanced the idea that elementary particles like electrons do not exist in stable or stationary conditions; they only exist in transitions and in interactions.

The ‘Copenhagen Interpretation’ further emphasised that a quantum particle can only be said to exist when it is observed, if it is not observed it does not exist. This was a revolutionary concept. Einstein could not reconcile with that idea. He retorted, “When the Moon is there in the sky, it is real; whether one observes it or not”. Thus, the great intellectual battle on the nature of reality ensued between Einstein and Bohr. Einstein firmly believed that the quantum mechanics as it existed in his life time was inconsistent and incomplete (although he withdrew the ‘inconsistent’ branding, as quantum mechanics kept explaining modern technical processes with consistency). To prove that ‘incompleteness’, he produced various ‘thought experiments’ at various times to challenge Bohr’s ‘Copenhagen Interpretation’. Bohr countered those challenges with technical explanations, but Einstein was not fully convinced.

Einstein
did not like the abstract nature of quantum mechanics. He always demanded that
theory must correspond to the reality, if not, it becomes a ‘voodoo’ science.

For his criticism, he was not very popular with the advocates of ‘Copenhagen Interpretation’. They even lamented that ‘how is it possible that Einstein who was the pioneer of quantum theory and who revolutionised gravitational concept by saying that space is warped by gravity and the gravitational field is indeed the space, now he is reluctant to accept ideas of quantum mechanics’?

Quantum mechanics had solved many intractable problems and predicted many physical aspects which subsequently came to be true. But at the same time, it is incomprehensible, extremely abstract and devoid of ‘elements of reality’. Anybody hoping to see theory mirroring reality would be totally disappointed. Even Richard Feynman, American Nobel laureate, who contributed significantly to the development of quantum physics once retorted, “I think I can safely say that nobody understands quantum mechanics”! Nonetheless, quantum mechanics is the most advanced scientific discipline of today.

Anthropogenic greenhouse gas emissions might be affecting more than just the climate. For the first time, scientists at NASA presented evidence that the orientation of the Earth’s spin axis is changing because of global warming.

The Earth spins from west to east about an axis once every 24 hours, creating the continuous cycle of day and night. The north-south spin axis runs through the North and South Poles and is tilted by 23.5 degrees from the vertical. The axial tilt causes almost all the seasonal changes.

But the tilt is far from constant. It varies between 21.6 and 24.5 degrees in a 41,000-year cycle. This variation together with small fluctuations in the Sun and Moon’s gravitational pull, oblate shape and elliptical orbit of the Earth, irregular surface, non-uniform distribution of mass and movement of the tectonic plates cause the spin axis, and hence the Poles, to wobble either east or west along its general direction of drift.

Until 2005, Earth’s spin axis has been drifting steadily in the southwest direction around ten centimetres each year towards the Hudson Bay in Canada. However, in 2005, the axis took an abrupt turn and started to drift east towards England at an annual rate of about 17 centimetres, according to data obtained by NASA’s Gravity Recovery and Climate Experiment satellites. It is still heading east.

After analysing the satellite data, scientists at NASA’s Jet Propulsion Laboratory in California attribute the sudden change in direction of the axis mainly to melting of Greenland’s ice sheets due to global warming. The reason: Melting of ice sheets and the resulting rise of the sea level are changing the distribution of mass on Earth, thereby causing the drift of the spin to change direction and become more oblique. The axis is particularly sensitive to changes in mass distribution occurring north and south of 45 degrees latitude. This phenomenon is similar to the shift in the axis of rotation of a spinning toy if we put more mass on one side of the top or the other.

Since 2002, ice sheets of Greenland have been melting at an annual rate of roughly 270 million tonnes. Additionally, some climate models indicate that a two-to-three degrees Celsius rise in temperature would result in a complete melting of Greenland’s ice sheets. If that happens, it could release the equivalent of as much as 1,400 billion tonnes of carbon dioxide, enhancing global warming even further. It would also raise the sea level by about 7.5 meters. By then, the wobbling of the Poles would also be completely out of whack.

The ice in the Arctic Ocean has also decreased dramatically since the 1960s. For every tonne of carbon dioxide released into the atmosphere, about three square meters of Arctic’s ice were lost in the last 50 years. This reflects a disquieting long-term trend of around ten percent loss of ice per decade. Furthermore, Antarctica is losing more ice than is being replaced by snowfall. The influx of water from the melting of ice of the Arctic Ocean and Antarctica together with the melting of glaciers and the subsequent redistribution of water across the Earth is also causing our planet to pitch over.

What does this mean for us? Although something as small as we humans shook up something as massive as the Earth, it won’t turn upside down as long as the Moon, which acts as a stabiliser of the Earth’s spinning motion, stays in the sky as our nearest neighbour. However, if the shift of the spin axis maintains its present rate and direction, then by the end of this century, the axis would shift by nearly 14 meters. Such a large shift will have devastating consequences for climate change and our planet.

The orientation of the Earth’s spin axis determines the seasonal distribution of radiation at higher latitudes. If the axial tilt is smaller, the Sun does not travel as far north in the sky during summer, producing cooler summers. A larger tilt, as could be in the future, would mean summer days that would be much hotter than the present summer days. In addition, it would impact the accuracy of GPS and other satellite-dependent devices.

Since global warming is causing the Earth’s mass to be redistributed towards the Poles, it would cause the planet to spin faster, just as an ice skater spins faster when she pulls her arms towards her body. Consequently, the length of a day would become shorter.

Our biological clock that regulates sleeping, walking, eating, and other cyclic activities is based on a 24-hour day. Faced with a shorter day, these circadian rhythms would be hopelessly out of sync with the natural world. Moreover, a rapidly spinning Earth will be unstable to the extent that the Poles would wobble faster. This would create enormous stress on the Earth’s geology leading to large-scale natural disasters that will most likely be disastrous for life on Earth.

We may not witness the effects of a rapidly spinning Earth by the end of this century or the next. Nevertheless, the effects will be perceivable a few centuries from now if the global temperature keeps on rising and the ice sheets keep on melting in tandem.

The shift in the Earth’s spin axis due to climate change highlights how real and profoundly large impact humans are having on the planet. The dire consequences of the shift in the axial tilt towards a larger obliquity, as noted above, is not a wake-up call, but an alarm bell. There is still time for our leaders to listen to the scientists and formulate a long-term approach to tackle the problem of climate change instead of a short-term Band-Aid approach, as outlined in the 2015 Paris Agreement, which will see us through only to the end of this century. Therefore, our foremost goal before the death knell should be to reverse global warming, or at the least, to stop further warming instead of limiting it to 1.5-degree in the next 75 years or so.

The author, Quamrul Haider, is a Professor of Physics at Fordham University, New York.

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